Microphone support structure



Aug. 23, 1960 R. K. DUNCAN 2,950,360

MICROPHONE SUPPORT STRUCTURE Filed Nov. 27, 1956 2 Sheets-Sheet 1 Aug. 23, 1960 R. K. DUNCAN 5 MICROPHONE SUPPORT STRUCTURE Filed Nov. 27, 1956 2 Sheets-Sheet 2 MICROPHONE SUPPORT STRUCTURE Robert Kern Duncan, Cincinnati, Ohio, assignor to The Baldwin Piano Company, Cincinnati, Ohio, 2: corporation of Ohio Filed Nov. 27, 1956, Ser. No. 624,523

11 Claims. (Cl. 179-146) The present invention relates to microphone structure, and more particularly to a microphone and support structure for use in a facial mask.

Oxygen masks are used by pilots of certain types of aircraft, and these masks are generally fitted with microphones. In assimilating data for the variation in facial contours, it has been found that an attempt to standardize on a single type of oxygen mask requires adjustment of the position of the microphone which has a variation as much as 1.4 inches. Hence, for optimum performance a microphone should be adjustably positioned to cover this range.

In microphones for oxygen masks, there are a number of other factors which require consideration. It is desirable to have a pressure gradient microphone which will cancel certain extraneous noises. The microphone,

therefore, must have a relatively free sound path to both 7 sides of the microphone diaphragm. The microphone should be capable of adjustment in position without the use of tools and, when once adjusted, should have suflicient rigidity to prohibit malpositioning through accidental shocks and jars. Yet, in the case of an emergency where the microphone is pushed into the face, the supporting means should collapse as much as possible so as to minimize the infliction of damage to the face. Electrical conductors to the microphone extending to the exterior of the mask should also be protected and preferably shielded, and yet occupy a minimum of space.

in microphones for oxygen masks, it has been customary to seal the acoustic paths to the diaphragm with an acoustic window which will prohibit the passage of moisture and yet be relatively transparent to the passage of sound waves. If the sealed microphone is not vented, there may be undesirable static air pressure loading which can result in a rupture of the moisture barrier. Furthermore, in a completely sealed unit small leaks invariably occur, and in time moisture is entrapped within the unit which has deleterious effects. Thus, there is presented a delicate problem of providing adequate venting means for a microphone of this type.

A solution to the various factors which must be considered in microphones for facial masks has been found by the present invention whereby a single means serves as an adjustable support, a shielded conduit for the electrical conductors, provides a vent to a sealed microphone and provides a certain control of the response characteristics of the microphone. It therefore is an object of the present invention to provide a microphone support which is adjustable within a facial mask.

Another object of the invention is to provide an improved microphone support which connects the inside of a moisture sealed microphone to the atmosphere exterior to the mask.

Another object of the invention is to provide an improved combined microphone support, electrical conduit and air passage.

Still another object of the invention is to provide a 2,950,360 Patented Aug. 23, 19 60 microphone support which also serves to control the response characteristics of the microphone.

A further object of the invention is to provide improved means for controlling the coupling between two sides of a microphone diaphragm.

A still further object of the invention is to provide in a mask, a microphone mounting venting the microphone to the exterior of the mask so that the differential pressure at the microphone is no greater than that existing between the pressure within the mask and that exterior to the mask.

Other and further objects of the invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a diagrammatic representation of a faci oxygen mask equipped with the microphone structure and support comprising the present invention;

Figure 2 is a perspective View of the microphone structure and support of the present invention;

Figure 3 is a detail longitudinal cross-sectional view of the microphone and support of Figure 2;

Figure 4 is an exploded cross-sectional partly diagrammatic view of the microphone; and

Figure 5 is the equivalent electric circuit diagram of the microphone.

In Figure 1 there is illustrated an oxygen mask 11 adapted to fit over the nose, mouth and a portion of the chin of a human face 12;. The oxygen mask is connected to a hose 13 which fits onto a valve 14 within the mask ll. On the exterior of the mask there isan electric conductor cable 15 which is connected to a support member 16 fitted into an aperture in the mask '11 so as to extend between the exterior and interior surfaces of the mask. On the interior side of the support 16, there is a tube 17 which is bendable so as to adjustably position a microphone l8.

Further details of the support and microphone assembly are shown in the perspective view of Figure 2. In the original installation, the tube 17 is generally firstformed with a small loop which then is changed in order to position the microphone at the proper distance from the ips. This generally is a short distance away so that the microphone could be touched by pursing or protruding the lips.

Certain details of the microphone and support assembly are best illustrated in Figure 3. The microphone 18 comprises a cylindrical casing 21 having two flat end members 22, each of which is provided with a series of perforations or holes 23 arranged in a circle so as to appear as viewed in Figure 2. The casing 21 is divided into two chambers 24 and 25 by a diaphragm 26 which is retained in position by suitable annular spacing members 27 and 28. At the center of the microphone, two permanent magnet pole pieces 2? and 31 are located close to the diaphragm 26. Surrounding the pole pieces 29 and 31 are coil windings 32 and 33 which are connected in series by a conductor 34. Spaced from the end members 22 by annular rings 35 are acoustically transparent windows 36 which, however, serve as moisture barriers. These acoustically transparent windows 36 are of a suitable plastic film, such as Mylar.

It will be noted that the cylindrical casing 21 is joined to the bendable tube 17 preferably by soldering. The tube 17 is closed at one end by a cap or suitable closure 37. The compartment 24 is connected by a passage 38 to the interior of the tube :17. The compartment 25 is connected by a passage 39 to the interior of the tube 17'. The series conductor 34 passes through the passages '38 and 39 and a portion of the tube 17. 'Additional conductors extend from the windings 32 and 33 through the tube 17 to suitable electrical terminals 41 provided in the support member 16. The terminals 41 are connected to the conductors of the cable 15. The tube 17 extends through the support 16 so that its interior communicate s with the exterior of the mask; through an aperture 42 in one of the plates of 'the'mounting member 16. The tube 17 provides a vent for the sealed microphone to the ambient atmosphere outside of the mask so that the differential pressure in the microphone can be no greater than that existing between the interior of the mask and the exterior of the mask.

A portion of the tube 17, which interconnects the passages 38 and 39 together with those passages, serves to provide the desired inertance, resistance and capacitance to provide a controlling action on the response characteristics of the microphone. This action is better understood by reference to Figures 4 and 5.

Figure 4 isan exploded cross-sectional view diagrammatically representing the principal components of the microphone structure shown in Figure 3. The sound wave pressure P1 strikes the front of the microphone and passes through or is transmitted by the acoustic window 36 which has a certain inertance, resistance and capacitance M R and C The space between the first acoustical window 36 and the perforated end wall 22 of the microphone casing is a capacitance C The perforations or annular passages 23 in the end wall have an inertan'ce and resistance M R These perforations in turn communicate with the chamber 24 which has a capacitance C The diaphragm has inertance, resistance and capacitance M R and C a The other chamber 25 has a capacitance C which is connected to the annular arranged perforations or passages in the other end wall denoted by M R These are in communication with the space between the end wall and the other acoustic window which has a capacitance C The back side of the microphone is covered by an acoustic window having inertance, resistance and capacitance M R and C and is subject to the back sound pressure P i In the equivalent electrical network representing the acoustical network of the microphone shown in Figure {1, the various inertances, resistances and capacitances have been shown in Figure 5 asv their electricalequivalents, i.e., inductances, resistances and capacitances. Z is the acoustical equivalent of the electrical load impressed across the electrical terminals of the microphone reflected back into the mecho-acoustic circuit,

e.g., the lower the value of the amplifier input impedance that the microphone is used'with, the greater becomes the apparent stilfness of the vibratile member. From the electrical diagram of Figure 5, it is readily apparent that a change in the values M R C obtained by a change in the dimensions of the passages 38 and 39 and the distance therebetween will produce a change in these values, which comprises a shunt circuit for a portion of the network shown in Figure 5, thereby changing the response characteristic of the microphone.

Accordingly, a single means comprising the support tube 17 serves as a portion of the means for controlling the response characteristics of the microphone and provides a suitable vent tothe ambient atmosphere outside of the mask, while the tube support provides physical protection and shielding to the electrical conductors and serves as an adjustable support for the microphone casing.

While ,for the purpose of illustrating and describing the present invention a particular embodiment has been shown in the drawings, it is to be understood that the invention is not to be limited thereby, since such variations and modifications are contemplated as may be commensurate with the spirit and scope of the invention as set forth in the accompanying claims.

I claim as my invention:

1. The combination comprising a facial mask, a support member in said. mask extendingfrom the exterior to the interior of said mask, an adjustably positiorfrled air tube secured to the interior side of said support member, said air tube communicating with the exterior of said support member, and a sealed microphone having' a vibratile diaphragm, said microphone being mounted adjacent the end of said tube and having two chambers each connected to said tube.

2. The combination comprising a facial mask, a sup port member in said mask extending from the exterior to the interior of said mask, a bendable adjustably positioned metal air tube secured at one end to the interior I are provided with passages to said tube to control the coupling between said two chambers.

4. The combination of claim 1 together with electrical conductors extending from said microphone through said tube to the exterior of said mask.

5. The combination of a facial mask having a support member therein extending from the exterior to the interior of said mask, a bendable air tube secured at one end to said support member, said air tube communicating with the exterior of said mask, a moisture sealed difierential microphone mounted at the other end of said tube, said microphone having a diaphragm dividing said microphone into two chambers each connected to said tube so that the difierential pressure at the microphone is no greater than that existing between the pressure within the mask and that exterior to the mask, and electrical conductors extending from the exterior .of said mask through said tube to the interior of said microphone.

6. A moisture sealed diiferential microphone for a facial mask comprising a cylindrical casing having a vibratile diaphragm dividing said casing into two chambers, electromagnetic members aranged on opposite sides of said diaphragm, the ends of said casing having perforations therein for sound pressure changes to impinge upon sald diaphragm, 'a moisture proof acousticwindow covering each end of said casing, a tube secured to the cylindrical side of said casing and arranged to extend to the exterior of said mask, and a passage from each chamber to said tube proportioned to control the response characteristics of said microphone and to provide an air vent for each chamber.

7. The combination of claim 6 wherein the size of said passages and the distance therebetween determine the inertance, resistance and capacitance of the air path between the two chambers.

8. The combination comprising a microphone having chambers on opposite sides of a diaphragm, and having electrical terminals, an air tube interconnecting said chambers and extending away from the microphone to serve as a support therefor, said tube being bendable to provide adjustable positioning of said microphone, and electrical conductors within said tube connected to the terminals of the microphone.

9. The combination of claim 8 wherein the distance of the passage between the chambers through said tube controls the response characteristics of the microphone.

10. A microphone comprising an air tight housing ineluding a sound permeable window, a vibratile magnetic diaphragm mounted confronting the sound permeable window in said housing and dividing the housing into two air tight chambers, a magnetic circuit including a magnet, the diaphragm, and a gap confronting the diaphragm, and an elongated tube mounted to the exterior of the housing and having separate passages extending therefrom to each of the chambers within the housing whereby the length and size of the tube and passages controls the frequency response characteristic of the microphone.

11. A sealed microphone comprising an air tight casing having a sound permeable window therein, an electromechanical transducer including a vibratile diaphragm mounted within the casing, the diaphragm dividing the casing into two air tight chambers, an air tube mounted on the exterior of the casing having two spaced passages, each of said passages extending from the air tube to one of the chambers within the casing.

References Cited in the file of this patent UNITED STATES PATENTS Berger June 30, 1914 Pitkin July 4, 1944 Bostwick et a1 July 30, 1946 Black et a1. Nov. 12, 1946 

